Radio stations have a generalized broadcast range that is typically defined by the area in which a broadcast radio signal remains strong enough for receipt and decoding by a receiver. Within a given broadcast range, however, a number of factors can cause interruptions and diminished signal strength. These include, for example, interfering signals from other broadcasts, terrain (man made and natural), weather and atmospheric conditions.
Determining the broadcast range of a particular station can be difficult, because many of the signal strength affecting conditions can vary on a day by day basis. There are certainly areas in which a signal is always received or never received, but for a significant portion of a broadcast range, especially around the outer edges, the variance in day-to-day transmission ranges can be significant. Because so many uncontrollable factors impact broadcast range, it can be difficult to determine even a rough edge of a range. This presents obstacles to defining a listening audience and station's “reach,” which in turn presents difficulties in advertising sales. Daily changes in which stations are available where may also frustrate drivers who travel frequently within the fringes of broadcast ranges.